1. Technical Field
This application relates to an improved failure sensing device for use in diaphragm pumps.
2. DESCRIPTION OF THE PRIOR ART
Diaphragm pumps are widely used in the chemical, petrochemical, process and other industries, as noted for example, in U.S. Pat. No. 3,285,182, which refers to such specific uses as in reagent feeding in reactor systems, replenishers and activators in photochemical and electro-chemical systems.
U.S. Pat. No. 3,666,379, teaches that when handling corrosive fluids, it is desirable to use a diaphragm disk which should be made of a chemically inert polymer such as polytetrafluroethylene (PTFE). The patent indicates that the previous inability to use PTFE can be overcome through the use of the disk referred to in the patent. Unfortunately, attack of the diaphragm by corrosives, fatigue or solvents still leads to the failure of the diaphragm.
The attempts to improve the physical design and chemistry of the material of construction of the diaphragm have lead to improvements. However, diaphragms still have a finite life span.
Devices in accordance with the prior art in the past have been known to exhibit certain shortcomings and problems. As noted in U.S. Pat. No. 3,816,034, mechanically or positively actuated diaphragm pumps suffer from: the disadvantage that the diaphragm, due to its positive mechanical connection to a reciprocating drive, is subject to a combination of high shear, bending and tension stresses in the operation of the pumping cycle. Such stresses then lead to shutdowns and replacement of the diaphragm when destruction thereof is imminent or has occurred.
The failure of the diaphragm is normally proceeded by the development of minute cracks, tears or hair line fissures which expand until there is a pathway completely through the diaphragm.
The problem associated with the replacement of a diaphragm after failure is that failure takes place when the diaphragm stress induced cracks open to the point where there is a hole completely through the diaphragm and consequently, there is a passage for the flow of liquid between the two pump chambers which are normally separated by the diaphragm. Thus, failure can result in heavy losses due to contamination of material streams, exposure of hardware to corrosives, and excessive down time. The fundamental problem is that it is essentially impossible to predict with accuracy the point in time at which the diaphragm will fail. Predictions are thus made on a statistical average basis, which means that some diaphragm will fail before the time period for periodic replacement and some diaphragm will be replaced prematurely, that is, before the major time period of their life span has been expended.